The recent introduction of WiMAX technology and other fourth-generation (4G) air-interface protocols promises to further increase the proliferation of wirelessly-equipped devices. WiMAX (Worldwide Interoperability for Microwave Access) is an Institute of Electrical and Electronics Engineers (IEEE) standard, designated 802.16, with the 802.16e being the current version of the standard (the terms “IEEE 802.16,” “IEEE 802.16e,” and “WiMAX” may be used interchangeably herein). WiMAX provides a robust mechanism for wireless communication between base stations and subscriber stations. In particular, WiMAX is designed to provide fixed, portable or non-line-of-sight service with a potential range of five miles, a throughput on the order of thirty megabits per second, and superior quality of service and security.
WiMAX chipsets that provide for communication in accordance with the WiMAX protocol are becoming increasingly prevalent as standard or optional equipment not only in traditional wireless communications devices, such as cellular phones and personal digital assistants, but also in devices that, heretofore, were not used for access to telephony networks. These devices include portable music players, entertainment devices such as game players, automobiles, domestic appliances and so on.
WiMAX networks are typically implemented as a macro cellular wireless networks (which may also be referred to as “macro networks”), which typically provide communication services such as voice, text messaging, and packet-data communication for WiMAX-capable mobile stations. Such mobile stations (which may also be referred to as access terminals, subscriber stations, or client devices, among other terms) and networks typically communicate with each other over a radio frequency (RF) air interface according to one or more wireless protocols (e.g. WiMAX, CDMA (Code Division Multiple Access), EV-DO (Evolution Data Optimized), and/or one or more others). Mobile stations typically conduct wireless communications with these networks via one or more base transceiver stations (base stations), each of which send communications to and receive communications from mobile stations over the air interface.
Each base station is in turn connected with a network entity known as a base station controller (BSC) (which may also be referred to as a radio network controller (RNC)), which controls one or more base stations and acts as a conduit between the one or more base stations and one or more switches or gateways, such as a mobile switching center (MSC) and/or a packet data serving node (PDSN). The one or more switches or gateways may then interface with one or more signaling and/or transport networks. As examples, an MSC may interface with the public switched telephone network (PSTN), while a PDSN may interface with one or more core packet data networks and/or the Internet. As such, mobile stations can typically communicate over the one or more signaling and/or transport networks from anywhere inside the coverage area of one or more base stations, via the base station(s), a BSC, and a switch or gateway such as an MSC and/or PDSN.
In WiMAX, data communications between a mobile station and a base station (i.e. a base station, or combinations of one or more base stations and a BSC) are formatted as Orthogonal Frequency-Division Multiplexed (OFDM) symbols, which are further organized into data frames. As some WiMAX systems employ Transmit Division Duplexing, all base stations in a given market typically begin their transmissions at the same. In particular, the base stations in a given coverage area all begin transmitting each frame at substantially the same time, a concept which is referred to herein as “frame-start synchronization.” As there is a five millisecond (ms) frame interval (i.e., each frame has a duration of five ms), this means that the transmitters of each base station turn off and on twenty times per second.
To achieve frame-start synchronization, existing WiMAX base stations all receive a highly-accurate and stable timing signal that is available via a Global Positioning System (GPS) satellite. Since base stations may be of varying distances from a GPS satellite, the delay experienced by a GPS timing signal between the GPS satellite and different base stations may vary as well. Accordingly, each WiMAX base stations typically apply an offset to the GPS reference signal that is based on the delay between the base station and the GPS satellite. By adjusting the GPS timing signal as such, nearby WiMAX base stations are essentially using the same timing signal to control their frame transmissions, and thus are able to synchronize frame-start timing with each other.